/*
 * Copyright (C) 2005 Luca Veltri - University of Parma - Italy
 *
 * This file is part of MjSip (http://www.mjsip.org)
 *
 * MjSip is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * MjSip is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with MjSip; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * Author(s):
 * Luca Veltri (luca.veltri@unipr.it)
 */

package org.zoolu.tools;



/** Simple and fast hash/message-digest algorithm.
 */
public class SimpleDigest extends MessageDigest
{

    // ************************* Attributes *************************

    /** The digest */
    byte[] message_digest;

    /** Whether is finalized. */
    boolean is_done;

    /** Index within the message_digest. */
    int index;

    /** Add term */
    byte add_term;


    // *********************** Public methods ***********************

    /** Constructor */
    public SimpleDigest(int size)
    {  init(size);
    }


    /** Constructor */
    public SimpleDigest(int size, byte[] buffer)
    {  init(size);
        update(buffer);
    }


    /** Constructor */
    public SimpleDigest(int size, byte[] buffer, int offset, int len)
    {  init(size);
        update(buffer,offset,len);
    }


    /** Constructor */
    public SimpleDigest(int size, String str)
    {  init(size);
        update(str);
    }


    /** Inits the SimpleDigest */
    private void init(int size)
    {  is_done=false;
        message_digest=new byte[size];
        for (int i=0; i<size; i++) message_digest[i]=(byte)(i);
        index=0;
        add_term=0;
    }


    /** MessageDigest block update operation.
     * Continues a message-digest operation,
     * processing another message block, and updating the context. */
    public MessageDigest update(byte[] buffer, int offset, int len)
    {
        if (is_done) return this;
        //else

        for (int i=0; i<len; i++)
        {  if (index==message_digest.length) index=0;
            add_term+=buffer[offset+i];
            message_digest[index]=(byte)(message_digest[index]^add_term);
            index++;
        }
        return this;
    }


    /** MessageDigest finalization. Ends a message-digest operation, writing the
     * the message digest and zeroizing the context. */
    public byte[] doFinal()
    {
        if (is_done) return message_digest;
        //else

        int k=message_digest.length-index;
        while (index<message_digest.length)
        {  message_digest[index]=(byte)(message_digest[index]^(k));
            index++;
            k++;
        }
        for (int i=0; i<message_digest.length; i++) message_digest[i]=(byte)(message_digest[i]^add_term);

        return message_digest;
    }


    /** Calculates the SimpleDigest. */
    public static byte[] digest(int size, byte[] buffer, int offset, int len)
    {  MessageDigest md=new SimpleDigest(size,buffer,offset,len);
        return md.doFinal();
    }


    /** Calculates the SimpleDigest. */
    public static byte[] digest(int size, byte[] buffer)
    {  return digest(size,buffer,0,buffer.length);
    }


    /** Calculates the SimpleDigest. */
    public static byte[] digest(int size, String str)
    {  MessageDigest md=new SimpleDigest(size,str);
        return md.doFinal();
    }

}
